In order for two-factor authentication (2FA) to work via a changing number code when logging in to purchase online, the smartphone and web server must agree on the current time. If one of the clocks deviates significantly, the login and thus the order will fail.
The fact that networked devices know the correct time is also important for many other applications, for example online banking, e-car charging stations, networked production systems in industry or high-frequency trading on stock exchanges. For the latter, there is even an international agreement on the maximum permissible deviation.
In Germany, the Physikalisch-Technische Bundesanstalt (PTB) sets the legally binding time and disseminates it in three ways. As a classic, the long-wave transmitter DCF77 synchronizes radio clocks across Europe. The telephone time announcement still exists, but the most important path today is the Internet.
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